Re: What is difference between stable and unstable sorting algorithm?

Stable sort is when the sequence of "equal" elements before sorting remains the same after sorting.
Any unstable sorting algorithm can also be made stable if you also take into account the index of the element in list before it was sorted and compare equal elements using it.

Re: What is difference between stable and unstable sorting algorithm?

A sorting algorithm is said to be stable if two objects with equal keys appear in the same order in sorted output as they appear in the input unsorted array. whereas a sorting algorithm is said to be unstable if their are two or more objects with equal keys doesn't appear in same order before and after sorting.